// Source File Name:   Base64.java
package com.mouchina.base.utils;

public class Base64
{
    private static char[] Base64Code =
        {
            'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V',
            'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r',
            's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/'
        };
    private static byte[] Base64Decode =
        {
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, 63, -1, 63, 52, 53, 54, 55, 56, 57,
            58, 59, 60, 61, -1, -1, -1, 0, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18,
            19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39,
            40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1
        };

    private Base64(  )
    {
    }

    public static String encode( byte[] b )
    {
        int code = 0;
        StringBuffer sb = new StringBuffer( ( ( b.length - 1 ) / 3 ) << 6 );

        for ( int i = 0; i < b.length; i++ )
        {
            code |= ( ( b[i] << ( 16 - ( ( i % 3 ) * 8 ) ) ) & ( 255 << ( 16 - ( ( i % 3 ) * 8 ) ) ) );

            if ( ( ( i % 3 ) == 2 ) || ( i == ( b.length - 1 ) ) )
            {
                sb.append( Base64Code[( code & 0xfc0000 ) >>> 18] );
                sb.append( Base64Code[( code & 0x3f000 ) >>> 12] );
                sb.append( Base64Code[( code & 0xfc0 ) >>> 6] );
                sb.append( Base64Code[code & 0x3f] );
                code = 0;
            }
        }

        if ( ( b.length % 3 ) > 0 )
        {
            sb.setCharAt( sb.length(  ) - 1, '=' );
        }

        if ( ( b.length % 3 ) == 1 )
        {
            sb.setCharAt( sb.length(  ) - 2, '=' );
        }

        return sb.toString(  );
    }

    public static byte[] decode( String code )
    {
        if ( code == null )
        {
            return null;
        }

        int len = code.length(  );

        if ( ( len % 4 ) != 0 )
        {
            throw new IllegalArgumentException( "Base64 string length must be 4*n" );
        }

        if ( code.length(  ) == 0 )
        {
            return new byte[0];
        }

        int pad = 0;

        if ( code.charAt( len - 1 ) == '=' )
        {
            pad++;
        }

        if ( code.charAt( len - 2 ) == '=' )
        {
            pad++;
        }

        int retLen = ( ( len / 4 ) * 3 ) - pad;
        byte[] ret = new byte[retLen];

        for ( int i = 0; i < len; i += 4 )
        {
            int j = ( i / 4 ) * 3;
            char ch1 = code.charAt( i );
            char ch2 = code.charAt( i + 1 );
            char ch3 = code.charAt( i + 2 );
            char ch4 = code.charAt( i + 3 );
            int tmp =
                ( Base64Decode[ch1] << 18 ) | ( Base64Decode[ch2] << 12 ) | ( Base64Decode[ch3] << 6 ) |
                Base64Decode[ch4];
            ret[j] = (byte) ( ( tmp & 0xff0000 ) >> 16 );

            if ( i < ( len - 4 ) )
            {
                ret[j + 1] = (byte) ( ( tmp & 0xff00 ) >> 8 );
                ret[j + 2] = (byte) ( tmp & 0xff );

                continue;
            }

            if ( ( j + 1 ) < retLen )
            {
                ret[j + 1] = (byte) ( ( tmp & 0xff00 ) >> 8 );
            }

            if ( ( j + 2 ) < retLen )
            {
                ret[j + 2] = (byte) ( tmp & 0xff );
            }
        }

        return ret;
    }
}
